The present invention relates to an OCB-mode liquid crystal display device with fast response and broad viewing angle for displaying TV images, personal computer or multimedia images, a manufacturing method for the same, and a driving method for a liquid crystal display device.
Conventional liquid crystal display devices employ, as one example of liquid crystal display modes, twisted nematic (TN) mode liquid crystal display elements using a nematic liquid crystal with positive dielectric anisotropy, but these have the shortcomings of a slow response and narrow viewing angles. There are also display modes with slow response and broad viewing angles, using a ferroelectric liquid crystal (FLC) or anti-ferroelectric liquid crystal, but these have shortcomings with regard to burn-in, shock resistance, and temperature dependence. There is also the in-plane switching (IPS) mode which has extremely broad viewing angles, in which the liquid crystal molecules are driven within the display plane by a transversal electric field, but the response times are slow, and numerical aperture and luminance are low. When trying to display full-color moving images on large screens, a liquid crystal mode with broad viewing angle, high luminance and fast display properties is necessary, but at present, a liquid crystal display mode that perfectly satisfies all these requirements in practice does not exist.
Among the conventional liquid crystal display devices that aimed for at least a broad viewing angle and high luminance are liquid crystal display devices in which TN mode liquid crystal regions are partitioned into two domains to widen the viewing angle vertically (see SID 92 DIGEST p.798-801). That is to say, using a nematic liquid crystal with positive dielectric anisotropy in the display pixels of the liquid crystal display device, two TN mode liquid crystal regions with different alignment orientation of the liquid crystal molecules are formed, and the viewing angle is enlarged by this TN-mode with two alignment domains.
FIG. 48 is a diagram showing the configuration of such a conventional liquid crystal display device. In FIG. 48, numerals 701 and 702 denote glass substrates, numerals 703 and 704 denote electrodes, and numerals 705, 705xe2x80x2, 706, and 706xe2x80x2 denote alignment films. In the alignment region A, the nematic liquid crystal molecules 707 and 707xe2x80x2 with positive dielectric anisotropy are slightly tilted away from the upper and lower boundaries to the opposing substrates, forming a larger and a smaller pretilt angle, whereas in the other alignment region B, the size of the pretilt angles with respect to the upper and lower boundaries of the opposing substrates is opposite to that in the alignment region A. Both the larger and the smaller pretilt angles are several degrees each, and are set to different angles. An example of a conventional manufacturing method for forming alignment regions with different pretilt angles at the upper and lower substrates is spreading photoresist on an alignment film, masking the photoresist photolithographically, and rubbing the desired alignment film surface in a predetermined direction, and repeating this procedure a certain number of times. As shown in FIG. 1, with this configuration, the liquid crystal molecules in the central portions of the liquid crystal layer in the alignment regions A and B are provided with opposite orientations, and since the liquid crystal molecules of the alignment regions rise in different directions when a voltage is applied, the refractive index anisotropy with respect to incoming light evens out for each pixel, and the viewing angle can be enlarged. With this conventional TN-mode with two alignment domains, the viewing angle can be made wider than with regular TN-mode, and the vertical viewing angle becomes about xc2x135xc2x0 at a contrast of 10.
However, the response time is substantially the same as in TN-mode, namely about 50 ms. Thus., in this conventional TN-mode with two alignment domains, viewing angle and response are insufficient.
As for liquid crystal display modes utilizing the so-called homeotropic alignment mode, in which the liquid crystal molecules are aligned approximately vertically at the boundaries to the alignment films, there are liquid crystal display devices with broad viewing angle and fast response that are provided with film phasexe2x80x94difference plates and subjected to alignment partitioning, but again the response time between black and white display is about 25 ms, and in particular the response time for gray scales is slow at 50-80 ms, which is longer than the {fraction (1/30)}s that are held to be the visual speed of the human eye, so that moving images appear blurred.
On the other hand, a bend alignment type liquid crystal display device (OCB-mode liquid crystal display device) has been proposed, which utilizes changes of the refractive index due to changes in the angle with which the liquid crystal molecules rise when the liquid crystal molecules between the substrates are in bend alignment. The speed with which the orientation of bend aligned liquid crystal molecules changes in the ON state and the OFF state is much faster than the speed of orientation changes between ON and OFF states in TN liquid crystal display devices, so that a liquid crystal display device with fast response time can be obtained. Moreover, in this bend alignment type liquid crystal display device, optical phase differences can be compensated automatically, because all the liquid crystal molecules are bend aligned between the upper and lower substrates, and the liquid crystal display device has potential as a liquid crystal display device with low voltage and broad viewing angle, because phase differences are compensated by the film phase difference plates.
Incidentally, these liquid crystal display devices are manufactured such that the liquid crystal molecules between the substrates are in splay alignment when no voltage is applied. In order to change the refractive index using bend alignment, the entire display portion has to be transitioned uniformly from splay alignment to bend alignment before use of the liquid crystal display device. When applying a voltage between the opposing display electrodes, the transition seeds for the transition from splay alignment to bend alignment do not appear in uniform distribution, but around the distributed spacers, at alignment irregularities at the boundary to the alignment films, or at damaged portions. Furthermore, the transition seeds do not necessarily appear always at the same locations, which may easily lead to display defects, in which the transition sometimes takes place and sometimes does not take place. Consequently, it is very important that at least all pixel portions of the entire display portion are transitioned uniformly from splay alignment to bend alignment before use.
However, conventionally, when applying a simple ac voltage, the transition sometimes does not take place, and when it does take place, the transition time is very long.
It is an object of the present invention bend alignment type liquid crystal display device with fast response, suitable for display of moving images and broad viewing angle, in which the transition into bend alignment takes place reliably, and the transition is concluded in short time so that there are no display defects, as well as a manufacturing method for such a liquid crystal display device, and a driving method for a liquid crystal display device.
To achieve this object, according to a first aspect of the invention, a method for driving a liquid crystal display device, for an alignment transition from splay alignment to bend alignment in a liquid crystal display device which includes a pair of substrates and a liquid crystal layer disposed between the substrates; wherein, when no voltage is applied, pretilt angles of the liquid crystal at an upper and at a lower boundary of the liquid crystal layer have opposite signs, and the liquid crystal layer is in splay alignment, having been subjected to a parallel alignment process; wherein, before liquid crystal display driving, an initialization process is performed, in which the alignment of the liquid crystal layer is transitioned from splay alignment to bend alignment by application of a voltage to the substrates; and wherein the liquid crystal display driving is performed in the bend alignment attained by this initialization;
includes applying to the substrates an ac voltage superimposed with a bias voltage to cause transition of the liquid crystal layer into bend alignment.
With this method, an ac voltage superimposed with a bias voltage is applied between the substrates, which makes the transition time shorter than when only an ac voltage is applied. The reason for this is that, superimposing a bias voltage has the effect that the alignment of the liquid crystal molecules in the liquid crystal layer is disturbed by the bias voltage, and the liquid crystal molecules lean toward one of the substrates. Thus, transition seeds appear within a short time and reliably in the liquid crystal layer, and the transition time is shortened. In addition, the transition time be made even shorter by increasing the effective voltage.
According to a second aspect of the invention, a driving method for an alignment transition from splay alignment to bend alignment in a liquid crystal display device which includes a pair of substrates and a liquid crystal layer disposed between the substrates; wherein, when no voltage is applied, pretilt angles of the liquid crystal at an upper and at a lower boundary of the liquid crystal layer have opposite signs, and the liquid crystal layer is in splay alignment, having been subjected to a parallel alignment process; wherein, before liquid crystal display driving, an initialization process is performed, in which the alignment of the liquid crystal layer is transitioned from splay alignment to bend alignment by application of a voltage to the substrates; and wherein the liquid crystal display driving is performed in the bend alignment attained by this initialization;
includes a step of applying to the substrates an ac voltage superimposed with a bias voltage, and a step of putting the substrates into an electrically released state, repeated in alternation so as to cause transition of the liquid crystal layer into bend alignment.
This configuration includes providing a period of an electrically released state after the application of the ac voltage, which has the effect that the alignment of the liquid crystal molecules in the liquid crystal layer is disturbed, and the liquid crystal molecules lean toward one of the substrates. Thus, transition seeds appear within a short time and reliably in the liquid crystal layer, and the transition time is shortened.
According to a third aspect of the invention, a driving method for an alignment transition from splay alignment to bend alignment in a liquid crystal display device which includes a pair of substrates and a liquid crystal layer disposed between the substrates; wherein, when no voltage is applied, pretilt angles of the liquid crystal at an upper and at a lower boundary of the liquid crystal layer have opposite signs, and the liquid crystal layer is in splay alignment, having been subjected to a parallel alignment process; wherein, before liquid crystal display driving, an initialization process is performed, in which the alignment of the liquid crystal layer is transitioned from splay alignment to bend alignment by application of a voltage to the substrates; and wherein the liquid crystal display driving is performed in the bend alignment attained by this initialization;
includes a step of applying to the substrates an ac voltage superimposed with a bias voltage, and a step of applying zero voltage or a low voltage to the substrates, repeated in alternation so as to cause transition of the liquid crystal layer into bend alignment.
This configuration includes a zero voltage or a low voltage application period after the application of the ac voltage, so that the effect of disturbing the alignment of the liquid crystal molecules in the liquid crystal layer is larger than in the second aspect of the present invention. Consequently, the effect that the liquid crystal molecules lean toward one of the substrates occurs in very little time. Thus, and the transition time becomes even shorter.
According to a fourth aspect of the invention, in a method for driving a liquid crystal display device in accordance with the third aspect, the ac voltage superimposed with the bias voltage is replaced with a dc voltage.
With this configuration, also when a dc voltage is applied instead of the ac voltage, there are periods in which zero voltage of a low voltage are applied after the application of this dc voltage, which cause disturbances of the liquid crystal alignment in the liquid crystal layer. Thus, the transition time can be shortened with this driving method, too.
According to a fifth aspect of the invention, in a method for driving a liquid crystal display device in accordance with the second aspect, the frequency of the voltage repeated in alternation is in the range of 0.1 Hz to 100 Hz, and the duty ratio of the voltage repeated in alternation is in the range of at least 1:1 to 1000:1.
Here, xe2x80x9cvoltage repeated in alternationxe2x80x9d is the voltage when the repetition of the ac voltage application period and the period of the electrically released that as a whole is taken as one voltage pattern. The following are the reasons for the limitation of the frequency and the duty of the voltage repeated in alternation.
When the frequency is smaller than 0.1 Hz, then there is almost no alternating repetition, so that the tilting of the liquid crystal molecule alignment caused by this alternating repetition stops. On the other hand, when the frequency is larger than 100 Hz, then the rate of the alternating repetition is too high and approximates an ac voltage, so that the tilting of the liquid crystal molecule alignment caused by this alternating repetition stops.
When the duty ratio of the repeatedly applied voltage is smaller than 1:1 (for example, 1:5), then the voltage applied to the liquid crystal layer is not sufficient. When the duty ratio is larger than 1000:1, then there is almost no alternated repetition, and the voltage is almost a dc voltage, so that the tilting of the liquid crystal molecule alignment caused by this alternating repetition stops.
According to a sixth aspect of the invention, in a method for driving a liquid crystal display device in accordance with the third aspect, the frequency of the voltage repeated in alternation is in the range of 0.1 Hz to 100 Hz, and the duty ratio of the voltage repeated in alternation is in the range of at least 1:1 to 1000:1.
The reasons for these limitations of the frequency and the duty ratio of the voltage repeated in alternation are the same as in the sixth aspect of the present invention.
According to a seventh aspect of the invention, in a method for driving a liquid crystal display device in accordance with the first aspect, the liquid crystal display device is an active matrix liquid crystal display device, and wherein the ac voltage is applied between a pixel electrode of the active matrix liquid crystal display device that is coupled to a switching element formed on one of the substrates and a common electrode formed on the other substrate.
With this configuration, the transition time can be shortened in an active matrix liquid crystal display device.
According to an eighth aspect of the invention, in a method for driving a liquid crystal display device in accordance with the third aspect, the liquid crystal display device is an active matrix liquid crystal display device, and wherein the ac voltage is applied between a pixel electrode of the active matrix liquid crystal display device that is coupled to a switching element formed on one of the substrates and a common electrode formed on the other substrate.
With this configuration, the transition time can be shortened in an active matrix liquid crystal display device.
According to a ninth aspect of the invention, in a method for driving a liquid crystal display device in accordance with the eighth aspect, the ac voltage is applied to the common electrode.
With this configuration, the transition time can be shortened.
According to a tenth aspect of the invention, in a method for driving a liquid crystal display device in accordance with the fourth aspect, the liquid crystal display device is an active matrix liquid crystal display device, and wherein the dc voltage is applied between a pixel electrode of the active matrix liquid crystal display device that is coupled to a switching element formed on one of the substrates and a common electrode formed on the other substrate.
With this configuration, the transition time can be shortened in an active matrix liquid crystal display device.
According to an eleventh aspect of the invention, in a method for driving a liquid crystal display device in accordance with the tenth aspect, the dc voltage is applied to the common electrode.
With this configuration, the transition time can be shortened.
According to a twelfth aspect of the invention, in a method for driving a liquid crystal display device in accordance with the first aspect, the value of the ac voltage is set to a critical voltage that is a minimum voltage necessary for transitioning the liquid crystal layer from splay alignment to bend alignment.
With this configuration, it is possible to reduce the voltage.
According to a thirteenth aspect of the invention, in a method for driving a liquid crystal display device in accordance with the fourth aspect, the value of the ac voltage is set to a critical voltage that is a minimum voltage necessary for transitioning the liquid crystal layer from splay alignment to bend alignment.
With this configuration, it is possible to reduce the voltage.
According to a fourteenth aspect of the invention, in a method for driving a liquid crystal display device in accordance with the third aspect, the voltage is an alternated voltage averaging over time.
With this configuration, deterioration of the liquid crystal can be prevented.
According to a fifteenth aspect of the invention, a liquid crystal display device including a pair of substrates and a liquid crystal layer disposed between the substrates; wherein, when no voltage is applied, pretilt angles of the liquid crystal at an upper and at a lower boundary of the liquid crystal layer have opposite signs, and the liquid crystal layer is in splay alignment, having been subjected to a parallel alignment process; wherein, before liquid crystal display driving, an initialization process is performed, in which the alignment of the liquid crystal layer is transitioned from splay alignment to bend alignment by application of a voltage to the substrates; wherein the liquid crystal display driving is performed in the bend alignment attained by the initialization;
including a voltage application means for applying to the substrates an ac voltage or a dc voltage superimposed with a bias voltage, so as to transition the liquid crystal layer from splay alignment to bend alignment.
With this configuration, a liquid crystal display device with short transition time is accomplished.
According to a sixteenth aspect of the invention, in a liquid crystal display device as in the fifteenth aspect, the value of the ac voltage or dc voltage is set to a critical voltage that is a minimum voltage necessary for transitioning the liquid crystal layer from splay alignment to bend alignment.
With this configuration, a liquid crystal display device with short transition time is accomplished.
According to a seventeenth aspect of the invention, an active matrix liquid crystal display device including an array substrate provided with a pixel electrode; an opposing substrate provided with a common electrode; and a liquid crystal layer arranged between the array substrate and the opposing substrate; wherein pretilt angles of the liquid crystal at an upper and at a lower boundary of liquid crystal layer have opposite signs, and in a liquid crystal cell in splay alignment, which has been subjected to a parallel alignment process, the liquid crystal is in splay alignment when no voltage is applied; wherein, before liquid crystal display driving, an initialization process is performed, in which the alignment of the liquid crystal layer is transitioned from splay alignment to bend alignment by application of a voltage; wherein the liquid crystal display driving is performed in the bend alignment attained by the initialization;
including:
a liquid crystal cell including at least a first liquid crystal cell region, wherein a liquid crystal pretilt angle at an alignment film formed on an inner side of the array substrate is a first pretilt angle, and wherein a liquid crystal pretilt angle at an alignment film formed on an inner side of the opposing substrate is a second pretilt angle larger than the first pretilt angle; and a second liquid crystal cell region arranged next to the first liquid crystal cell region within the same pixel; wherein a liquid crystal pretilt angle at an alignment film formed on an inner side of the array substrate is a third pretilt angle, and wherein a liquid crystal pretilt angle at an alignment film formed on an inner side of the opposing substrate is a fourth pretilt angle larger than the third pretilt angle, the alignment films having been subjected to an alignment process directed from the first liquid crystal cell region to the second liquid crystal cell region;
a first voltage application means for applying a first voltage between the pixel electrode and the common electrode so as to form a disclination line at a border between the first liquid crystal cell region and the second liquid crystal cell region; and
a second voltage application means for creating transition seeds at the disclination line by applying a second voltage larger than the first voltage between the pixel electrode and the common electrode, and causing transition from splay alignment to bend alignment.
With this configuration, applying a first voltage between the pixel electrode and the common electrode forms a disclination line between the first liquid crystal cell region and the second liquid crystal cell region, where the bending energy is higher than around it, and applying a second voltage larger than the first voltage between the pixel electrode and the common electrode, directs even more energy to this disclination line, causing transition from splay alignment to bend alignment at the disclination line.
Consequently, in a liquid crystal display device with this configuration, the splayxe2x80x94bend alignment transition occurs reliably at a certain location (namely at the disclination lines) within the pixel regions provided with many liquid crystal cells, a reliable and fast alignment transition can be ensured, and a high-quality and inexpensive liquid crystal display device without display defects can be realized.
According to an eighteenth aspect of the invention, in a liquid crystal display device as in the seventeenth aspect, the first and the fourth pretilt angles are at most 3xc2x0, and the second and third pretilt angles are at least 4xc2x0.
With this configuration, the ratio between the second and the fourth pretilt angle, and the ratio between the first and the fourth pretilt angle can be large, so that disclination lines with a bending energy that is even higher than the bending energy around them can be formed, and the transition time from splay alignment to bend alignment can be made even shorter.
According to a nineteenth aspect of the invention, in a liquid crystal display device as in the seventeenth aspect, the direction in which the alignment films are subjected to the alignment process is perpendicular to signal electrode lines or gate electrode lines arranged along the pixel electrode.
With this configuration, a transversal electric field is applied from the transversal electric field application portions in a direction that is substantially perpendicular to the alignment of the liquid crystal molecules in the liquid crystal layer, so that this transversal electric field exerts a twisting force on the liquid crystal molecules, and consequently, transition seeds appear at the disclination line, and a quick alignment transition from splay alignment to bend alignment can be achieved.
According to a twentieth aspect of the invention, in a liquid crystal display device as in the seventeenth aspect, the direction in which the alignment films are subjected to the alignment process is slightly askew to a direction perpendicular to signal electrode lines or gate electrode lines arranged along the pixel electrode.
Making the direction in which the alignment films are subjected to the alignment process is slightly askew to a direction perpendicular to signal electrode lines or gate electrode lines arranged along the pixel electrode, a slightly askew transversal electric field is applied to the disclination lines from the signal electrode lines or gate electrode lines, so that the twisting force on the splay aligned liquid crystal molecules is increased, thereby assisting the transition to bend alignment.
According to a twenty-first aspect of the invention, in a liquid crystal display device as in the seventeenth aspect, the second voltage is pulse-shaped with a frequency in the range of 0.1 Hz to 100 Hz, and a duty ratio in the range of at least 1:1 to 1000:1.
Applying such a pulse-shaped second voltage and alternating voltage application periods and periods in which no voltage is applied, the liquid crystal molecules are disturbed and transition more readily, so that the splay aligned liquid crystal molecules transition into bend alignment. Frequency and duty ratio are limited to the above ranges to enlarge the transition regions of transition from splay alignment to bend alignment.
According to a twenty-second aspect of the invention, in a liquid crystal display device as in the seventeenth aspect, the gate electrode lines are in an ON state for at least most of said transition period.
The regions of the disclination lines have a bending energy that is higher than in the regions around them, and in this situation, the transversal electric field is applied to the disclination lines from the gate electrode lines, which are arranged transversally with respect to the pixel electrodes, so that even more energy is directed to them, and the transition from splay alignment to bend alignment is accelerated.
According to a twenty-third aspect of the invention, a liquid crystal display device as in the seventeenth aspect further includes a liquid crystal cell that has been alignment partitioned by irradiating UV light on a portion of at least one of the alignment films formed on the inner sides of the pixel electrode and the common electrode so that the pretilt angle of the liquid crystal at that alignment film is changed.
Irradiating UV light on a portion of the alignment films, it is possible to modify the surface of the irradiated region of the alignment films, and to decrease the pretilt angle of the liquid crystal in the modified alignment films. The reasons why the pretilt angle in the alignment films are decreased by irradiation with UV light are not entirely clear at present, but it seems that the UV light breaks up side chains in the alignment surface. Thus, liquid crystal cells with alignment partitions can be formed by irradiation with UV light.
According to a twenty-fourth aspect of the invention, a liquid crystal display device as in the seventeenth aspect further includes a liquid crystal cell that has been alignment partitioned by irradiating a portion of the pixel electrode and a portion of the common electrode with UV light under an ozone atmosphere to flatten at least one of the portions of the pixel electrode and the common electrode has been flattened, and applying and baking an alignment film on the pixel electrode and the common electrode, so as to change the pretilt angle of the liquid crystal at the alignment film.
Irradiating a portion of the pixel electrode and a portion of the common electrode with UV light under an ozone atmosphere, the surfaces of the pixel electrode and the common electrode can be flattened, and consequently, liquid crystal cells with alignment partitions and varying pretilt angles of the liquid crystal at the alignment films can be formed by spreading the alignment films on the pixel electrode and the common electrode.
According to a twenty-fifth aspect of the invention, a method for manufacturing an active matrix liquid crystal display device including an array substrate provided with a pixel electrode; an opposing substrate provided with a common electrode; and a liquid crystal layer arranged between the array substrate and the opposing substrate; wherein pretilt angles of the liquid crystal at an upper and at a lower boundary of the liquid crystal layer have opposite signs, and in a liquid crystal cell in splay alignment, which has been subjected to a parallel alignment process, the liquid crystal is in splay alignment when no voltage is applied; wherein, before liquid crystal display driving, an initialization process is performed, in which the alignment of the liquid crystal layer is transitioned from splay alignment to bend alignment by application of a voltage; wherein the liquid crystal display driving is performed in the bend alignment attained by the initialization;
includes:
a preparation step of preparing a liquid crystal cell in splay alignment, which has been subjected to a parallel alignment process, wherein the pretilt angles of the liquid crystal at the upper and lower boundaries of the liquid crystal layer arranged between the array substrate provided with the pixel electrode and the opposing substrate provided with the common electrode have opposite signs;
a disclination line forming step of applying a first voltage for forming a disclination line between the pixel electrode and the common electrode, and forming a disclination line at a boundary between a first liquid crystal cell region and a second liquid crystal cell region; and
an alignment transition step for transition from splay alignment to bend alignment of applying a second voltage larger than the first voltage between the pixel electrode and the common electrode, and creating transition seeds at the disclination line at the boundary between the first liquid crystal cell region and the second liquid crystal cell region.
With this method, the splayxe2x80x94bend alignment transition occurs reliably at a certain location (namely at the disclination lines) within the pixel regions provided with many liquid crystal cells in the liquid crystal display device, and transition seeds appear reliably, because the bending energy at the disclination lines is higher than around them. Consequently, a reliable and fast alignment transition can be ensured, and a high-quality and inexpensive liquid crystal display device without display defects can be obtained.
According to a twenty-sixth aspect of the invention, in a method for manufacturing a liquid crystal display device as in the twenty-fifth aspect, the preparation step includes an alignment process step of arranging the liquid crystal molecules in one pixel region in b-splay alignment by subjecting them to an alignment process such that a pretilt angle of the liquid crystal on the pixel electrode side becomes smaller than a pretilt angle of the liquid crystal on the common electrode side, and arranging the liquid crystal molecules in another pixel region in t-splay alignment by subjecting them to an alignment process such that a pretilt angle of the liquid crystal on the pixel electrode side becomes larger than a pretilt angle of the liquid crystal on the common electrode side.
With this method, b-splay alignment regions and t-splay alignment regions are formed in the pixels, and disclination lines are formed clearly at the border between them. As mentioned above, the bending energy at these disclination lines is larger than around them, so that transition seeds appear reliably, and consequently, a reliable and fast alignment transition can be ensured.
According to a twenty-seventh aspect of the invention, in a method for manufacturing a liquid crystal display device as in the twenty-sixth aspect, the alignment process step includes alignment partitioning by irradiating UV light on a portion of the alignment film formed on an inner surface side of at least one electrode of the pixel electrode and the common electrode to change the pretilt angle of the liquid crystal.
Irradiating UV light on a portion of the alignment films, it is possible to modify the surface of regions the alignment films irradiated with UV light, and to decrease the pretilt angle of the liquid crystal in the modified alignment films.
According to a twenty-seventh aspect of the invention, in a method for manufacturing a liquid crystal display device as in the twenty-sixth aspect, the alignment process step includes alignment partitioning by irradiating a region of at least one electrode of the pixel electrode and the common electrode with UV light under an ozone atmosphere, flattening a portion of the pixel electrode and the common electrode, and then applying and baking an alignment film on the pixel electrode and the common electrode to change the pretilt angle of the liquid crystal at the alignment film.
With this method, a portion of either the pixel electrode or the common electrode or both can be flattened, and consequently, a liquid crystal display device having liquid crystal cells with alignment partitions and varying pretilt angles of the liquid crystal at the alignment films can be formed by spreading the alignment films on the pixel electrode and the common electrode.
According to a twenty-ninth aspect of the invention, an active matrix liquid crystal display device includes an array substrate provided with a pixel electrode; an opposing substrate provided with a common electrode; and a liquid crystal layer arranged between the array substrate and the opposing substrate; wherein pretilt angles of the liquid crystal at an upper and at a lower boundary of liquid crystal layer have opposite signs, and in a liquid crystal cell in splay alignment, which has been subjected to a parallel alignment process, the liquid crystal is in splay alignment when no voltage is applied; wherein, before liquid crystal display driving, an initialization process is performed, in which the alignment of the liquid crystal layer is transitioned from splay alignment to bend alignment by application of a voltage; wherein the liquid crystal display driving is performed in the bend alignment attained by the initialization; and
wherein each pixel has at least one transition-inducing transversal field application portion due to which a transversal electric field is generated, and applying a continuous or intermittent voltage to the pixel electrode and the common electrode, transition seeds are created in each pixel, and the pixels transition from splay arrangement to bend arrangement.
The following effects can be attained with this configuration.
A voltage that is sufficiently larger than the transition voltage is applied between the pixel electrode and the common electrode, and at least one transition-inducing transversal electric application field portion provided in each pixel applies a transversal electric field, whereby the transversal electric application field portion becomes the starting point for the transition of the liquid crystal layer in the pixel from splay alignment to bend alignment (that is, it can be ensured that transition seeds appear in the liquid crystal layer near the transversal electric field application portions). Thus, the transition from splay alignment to bend alignment can be carried out fast.
According to a thirtieth aspect of the invention, in a liquid crystal display device as in the twenty-ninth aspect, the transversal electric field generated by the transversal electric field application portions is substantially perpendicular to the direction of the alignment process.
With this embodiment, the transversal electric field is applied by the transversal electric field application portions in a direction that is substantially perpendicular to the direction of the alignment of the liquid crystal molecules in the liquid crystal layer, so that this transversal electric field exerts a twisting force on the liquid crystal molecules, and consequently, transition seeds appear, and a quick transition from splay alignment to bend alignment can be achieved.
According to a thirty-first aspect of the invention, in a liquid crystal display device as in the twenty-ninth aspect, the transversal electric field application portions are electrode deformation portions, in which sides of the pixel electrodes are deformed to protrusions and recesses in a plane parallel to the substrate plane.
The following effects can be attained with this configuration.
The electric field concentrates between the transversal electric field application portions, which are electrode deformation portions, in which sides of the pixel electrodes are deformed to protrusions and recesses in a plane parallel to the substrate plane, and signal electrode lines or gate electrode lines arranged beneath the transversal electric field application portions. Consequently, the transversal electric field generated like this is stronger than the transversal electric field generated between pixel electrodes without such transversal electric field application portions and the signal electrode lines or gate electrode lines. Consequently, with the transversal electric field generated due to the transversal electric field application portions, the appearance of seeds in the liquid crystal layer can be ensured, and a quick transition from splay alignment to bend alignment can be achieved.
According to a thirty-second aspect of the invention, in a liquid crystal display device as in the twenty-ninth aspect, the transversal electric field application portions are electrode line deformation portions, in which signal electrode lines or gate electrode lines are deformed to protrusions and recesses in a plane parallel to the substrate plane.
The following effect can be attained with this configuration.
The same effect as in the thirty-first aspect of the present invention is attained due to electrode line deformation portions at either one or both types of electrode lines.
According to a thirty-third aspect of the invention, in a liquid crystal display device as in the twenty-ninth aspect, the transversal electric field application portions are deformations in the electrodes and the electrode lines, in which sides of the pixel electrodes are deformed to protrusions and recesses in a plane parallel to the substrate plane, and in correspondence to these protrusions and recesses, signal electrode lines or gate electrode lines are deformed to protrusions and recesses in a plane parallel to the substrate plane.
The following effects can be attained with this configuration.
The same effect as in the thirty-first aspect of the present invention is attained with the transversal electric field application portions, which are deformations in the electrodes and the electrode lines, in which at least one side of the pixel electrodes is deformed to protrusions and recesses in a plane parallel to the substrate plane, and in correspondence to these protrusions and recesses, signal electrode lines or gate electrode lines or both are deformed to protrusions and recesses.
According to a thirty-fourth aspect of the invention, in a liquid crystal display device as in the twenty-ninth aspect, the transversal electric field application portions are transversal electric field application line deformation portions in transversal electric field application lines that are deformed to protrusions and recesses in a plane parallel to the substrate plane, wherein the transversal electric field application lines are arranged in a layer above or below at least one of signal electrode lines or gate electrode lines and in the same direction as these, separated from them by an insulting film, and wherein the transversal electric field application lines are connected to a driving circuit, to which also the signal electrode lines or gate electrode lines are connected.
With this configuration, the transversal electric field application lines are dedicated lines for transversal electric field application, and are arranged in a layer above or below at least one of signal electrode lines or gate electrode lines, separated from them by an insulting film, which leads to flexibility with regard to the shape of the protrusions and recesses, which can be formed for example continuously along the sides of the transversal electric field application lines. Furthermore, since the transversal electric field application lines overlap with the signal electrode lines or the gate electrode lines, there is little light absorption, and consequently the aperture ratio of the pixels does not decrease. Thus, a redundant design with a greater degree of freedom.
According to a thirty-fifth aspect of the invention, in a liquid crystal display device as in the thirty-fourth aspect, the transversal electric field application lines are disconnected from the driving circuit during regular liquid display after alignment transition.
With this configuration, the transversal electric field application lines are disconnected from the driving circuit during regular liquid display after alignment transition, so that no electric field is generated between the transversal electric field application portions formed in the transversal electric field application lines and the pixel electrodes. Consequently, disturbances in the alignment of the liquid crystal do not occur during regular liquid crystal display, so that a liquid crystal display device with superior liquid crystal display quality can be obtained.
According to a thirty-sixth aspect of the invention, an active matrix liquid crystal display device including an array substrate; an opposing substrate; and a liquid crystal layer arranged between the array substrate and the opposing substrate; wherein pretilt angles of the liquid crystal at an upper and at a lower boundary of liquid crystal layer have opposite signs, and in a liquid crystal cell in splay alignment, which has been subjected to a parallel alignment process, the liquid crystal is in splay alignment when no voltage is applied; wherein, before liquid crystal display driving, an initialization process for a transition from splay alignment to bend alignment is performed by application of a voltage; wherein the liquid crystal display driving is performed in the bend alignment attained by the initialization;
includes at least one of a pixel electrode and a common electrode, wherein a defect portion for application of a transition-inducing transversal electric field is formed at least at one location in each pixel.
The following effects can be attained with this configuration.
Having at least one of a pixel electrode and a common electrode in which a defect portion for application of a transition-inducing transversal electric field is formed at least at one location for each pixel unit, a bending of the electric field (that is, an oblique electric field) is generated at the edge of this defect portion. Consequently, this oblique electric field exerts a twisting force on the liquid crystal molecules, so that the appearance of transition seeds can be ensured, and a quick transition from splay alignment to bend alignment can be achieved.
According to a thirty-seventh aspect of the invention, an active matrix liquid crystal display device including an array substrate; an opposing substrate; and a liquid crystal layer arranged between the array substrate and the opposing substrate; wherein pretilt angles of the liquid crystal at an upper and at a lower boundary of liquid crystal layer have opposite signs, and in a liquid crystal cell in splay alignment, which has been subjected to a parallel alignment process, the liquid crystal is in splay alignment when no voltage is applied; wherein, before liquid crystal display driving, an initialization process for a transition from splay alignment to bend alignment is performed by application of a voltage; wherein the liquid crystal display driving is performed in the bend alignment attained by the initialization;
includes in each pixel a transition-inducing transversal electric field application portion; and
each pixel includes a first alignment region, wherein a pretilt angle of liquid crystal molecules in one region at a pixel electrode is a first pretilt angle, and a pretilt angle of liquid crystal molecules in the one region at a common electrode opposing the pixel electrode is a second pretilt angle larger than the first pretilt angle; and
a second alignment region, wherein a pretilt angle of liquid crystal molecules in another region of the pixel electrode is a third pretilt angle, and a pretilt angle of liquid crystal molecules in the other region of a common electrode opposing the pixel electrode is a fourth pretilt angle smaller than the third pretilt angle.
The following effects can be attained with this configuration.
Due to the effect of the transversal electric field application portions, the pretilt angle in the first alignment region differs from the pretilt angle the second alignment region, so that a disclination line is formed between the first alignment region and the second alignment region. This disclination line becomes the starting point for the alignment transition, so that the transition from splay alignment to bend alignment is enhanced.
According to a thirty-eighth aspect of the invention, a liquid crystal display device as in the twenty-ninth aspect further includes a pulse voltage application portion for applying to the common electrode and the pixel electrode a pulse-shaped voltage with a frequency the range of 0.1 Hz to 100 Hz, and a duty ratio in the range of at least 1:1 to 1000:1.
The following effects can be attained with this configuration.
Although there may be certain differences depending for example on size, shape and thickness of the liquid crystal layer, the frequency and the duty ratio of the pulse voltage application portion are limited to the above ranges so as to enlarge the regions of transition from splay alignment to bend alignment.
Applying such a pulse-shaped second voltage and alternating voltage application periods and periods in which no voltage is applied, the liquid crystal molecules are disturbed and transition more readily, so that the splay aligned liquid crystal molecules transition into bend alignment. Frequency and duty ratio are limited to the above ranges to enlarge the transition regions of transition from splay alignment to bend alignment.
According to a thirty-ninth aspect of the invention, a liquid crystal display device including a pair of substrates; a liquid crystal layer disposed between the substrates; and a phase compensator arranged on an outer side of the substrates; wherein, when no voltage is applied, pretilt angles of the liquid crystal at an upper and at a lower boundary of the liquid crystal layer have opposite signs, and the liquid crystal layer is in splay alignment, having been subjected to a parallel alignment process; wherein, before liquid crystal display driving, an initialization process is performed, in which the alignment of the liquid crystal layer is transitioned from splay alignment to bend alignment by application of a voltage; wherein the liquid crystal display driving is performed in the bend alignment attained by this initialization;
includes at least one region in the display pixels where the liquid crystal layer thickness is smaller than around it, and the strength of an electric field applied to the liquid crystal layer in this region is larger than the strength of an electric field applied to the liquid crystal layer around it.
With this configuration, more transition seeds appear at the portions where the electric field is strong, so that the transition time can be shortened.
According to a fortieth aspect of the invention, a liquid crystal display device including a pair of substrates; a liquid crystal layer disposed between the substrates; and a phase compensator arranged on an outer side of the substrates; wherein, when no voltage is applied, pretilt angles of the liquid crystal at an upper and at a lower boundary of the liquid crystal layer have opposite signs, and the liquid crystal layer is in splay alignment, having been subjected to a parallel alignment process; wherein, before liquid crystal display driving, an initialization process is performed, in which the alignment of the liquid crystal layer is transitioned from splay alignment to bend alignment by application of a voltage; and wherein the liquid crystal display driving is performed in the bend alignment attained by this initialization;
includes at least one region outside the display pixels where the liquid crystal layer thickness is small, and the strength of an electric field applied to the liquid crystal layer in this region is larger than strength of an electric field applied to the liquid crystal layer in the pixels.
With this configuration, electric field concentrations occur outside the pixels, and the transition seeds appearing outside the pixels are propagated into the pixels. Thus, also in this case, the transition time can be shortened.
According to a forty-first aspect of the invention, a liquid crystal display device including a pair of substrates; a liquid crystal layer disposed between the substrates; and a phase compensator arranged on an outer side of the substrates; wherein, when no voltage is applied, pretilt angles of the liquid crystal at an upper and at a lower boundary of the liquid crystal layer have opposite signs, and the liquid crystal layer is in splay alignment, having been subjected to a parallel alignment process; wherein, before liquid crystal display driving, an initialization process is performed, in which the alignment of the liquid crystal layer is transitioned from splay alignment to bend alignment by application of a voltage; wherein the liquid crystal display driving is performed in the bend alignment attained by this initialization;
includes at least one location in the display pixels where the electric field concentrates.
According to a forty-second aspect of the invention, in a liquid crystal display device as in the forty-first aspect; the location in the display pixels where the electric field concentrates is at a portion of either the display electrode or the common electrode that partially protrudes in thickness direction of the liquid crystal layer, or both.
Thus, electric field concentrations can be achieved with such a protruding display electrode configuration.
According to a forty-third aspect of the invention, a liquid crystal display device including a pair of substrates; a liquid crystal layer disposed between the substrates; and a phase compensator arranged on an outer side of the substrates; wherein, when no voltage is applied, pretilt angles of the liquid crystal at an upper and at a lower boundary of the liquid crystal layer have opposite signs, and the liquid crystal layer is in splay alignment, having been subjected to a parallel alignment process; wherein, before liquid crystal display driving, an initialization process is performed, in which the alignment of the liquid crystal layer is transitioned from splay alignment to bend alignment by application of a voltage; wherein the liquid crystal display driving is performed in the bend alignment attained by this initialization;
includes at least one location outside the display pixels where the electric field concentrates.
Providing such electric field concentration portions outside the display pixels, the transition seeds appearing outside the pixels propagate into the pixels. Thus, also in this case, the transition time can be shortened.
According to a forty-fourth aspect of the invention, in a liquid crystal display device as in the forty-third aspect, the location where the electric field concentrates is a portion of an electrode that partially protrudes in thickness direction of the liquid crystal layer.
According to a forty-fifth aspect of the invention, a liquid crystal display device including a pair of substrates; a liquid crystal layer disposed between the substrates; and a phase compensator arranged on an outer side of the substrates; wherein, when no voltage is applied, pretilt angles of the liquid crystal at an upper and at a lower boundary of the liquid crystal layer have opposite signs, and the liquid crystal layer is in splay alignment, having been subjected to a parallel alignment process; wherein, before liquid crystal display driving, an initialization process is performed, in which the alignment of the liquid crystal layer is transitioned from splay alignment to bend alignment by application of a voltage; wherein the liquid crystal display driving is performed in the bend alignment attained by this initialization; and
a portion of either the display electrode or the common electrode or both is provided with an aperture portion.
Also with this configuration, the transition time can be shortened.
According to a forty-sixth aspect of the invention, a liquid crystal display device as in the forty-fifth aspect is an active matrix liquid crystal display device provided with switching elements, and wherein the aperture portion is a conducting via hole electrically connecting pixel electrodes formed on a flattening film and the switching elements.
Also with this configuration, the transition time can be shortened.
According to a forty-seventh aspect of the invention, in a liquid crystal display device as in the thirty-ninth aspect, the phase compensator includes at least one phase compensator made of an optical medium with negative reflective index anisotropy whose main axes are in hybrid arrangement.
According to a forty-eighth aspect of the invention, in a liquid crystal display device as in the forty-seventh aspect, the phase compensator includes at least one positive phase compensator.
According to a forty-ninth aspect of the invention, a method for driving a liquid crystal display device includes applying an electric field to a liquid crystal disposed between a first substrate and a second substrate arranged in opposition, and transitioning the alignment of the liquid crystal into bend alignment;
wherein the splay elastic constant k11 of the liquid crystal is in the range of 10xc3x9710xe2x88x927dynxe2x89xa7k11xe2x89xa76xc3x9710xe2x88x927dyn; and
satisfying the relation 1.57 rad greater than |xcex81xe2x88x92xcex82|xe2x89xa70.0002 rad, wherein xcex81 is the absolute value of a pretilt angle of the liquid crystal with respect to the first substrate and xcex82 is the absolute value of a pretilt angle of the liquid crystal with respect to the second substrate.
With this configuration, it is possible to decrease the critical electric field for liquid crystal transition, and achieve a quick transition from the initial alignment of the liquid crystal molecules to the bend alignment.
According to a fiftieth aspect of the invention, a method for driving a liquid crystal display device including applying an electric field to a liquid crystal disposed between a first substrate and a second substrate arranged in opposition, and transitioning the alignment of the liquid crystal into bend alignment;
wherein the splay elastic constant k11 of the liquid crystal is in the range of 10xc3x9710xe2x88x927dynxe2x89xa7k11xe2x89xa76xc3x9710xe2x88x927dyn; and
wherein the electric field is a main electric field E0 applied uniformly over space, to which a secondary electric field E1 applied non-uniformly over space is superimposed, satisfying the relation 1.0 greater than E1xe2x88x92E0 greater than {fraction (1/100)}.
Also with this configuration, it is possible to decrease the critical electric field for liquid crystal transition, and achieve a quick transition from the initial alignment of the liquid crystal molecules to the bend alignment.
According to a fifty-first aspect of the invention, a method for driving a liquid crystal display device including applying an electric field to a liquid crystal disposed between a first substrate and a second substrate arranged in opposition, and transitioning the alignment of the liquid crystal into bend alignment;
satisfying the relation 1.57 rad greater than |xcex81xe2x88x92xcex82|xe2x89xa70.0002 rad, wherein xcex81 is the absolute value of a pretilt angle of the liquid crystal with respect to the first substrate and xcex82 is the absolute value of a pretilt angle of the liquid crystal with respect to the second substrate; and
wherein the electric field is a main electric field E0 applied uniformly over space, to which a secondary electric field E1 applied non-uniformly over space is superimposed, satisfying the relation 1.0 greater than E1xe2x88x92E0 greater than {fraction (1/100)}.
Also with this configuration, it is possible to decrease the critical electric field for liquid crystal transition, and achieve a quick transition from the initial alignment of the liquid crystal molecules to the bend alignment.
According to a fifty-second aspect of the invention, a method for driving a liquid crystal display device including applying an electric field to a liquid crystal disposed between a first substrate and a second substrate arranged in opposition, and transitioning the alignment of the liquid crystal into bend alignment;
wherein the splay elastic constant k11 of the liquid crystal is in the range of 10xc3x9710xe2x88x927dyn greater than k11 greater than 6xc3x9710xe2x88x927dyn; and
satisfying the relation 1.57 rad greater than |xcex81xe2x88x92xcex82|xe2x89xa70.0002 rad, wherein xcex81 is the absolute value of a pretilt angle of the liquid crystal with respect to the first substrate and xcex82 is the absolute value of a pretilt angle of the liquid crystal with respect to the second substrate; and
wherein the electric field is a main electric field E0 applied uniformly over space, to which a secondary electric field E1 applied non-uniformly over space is superimposed, satisfying the relation 1.0 greater than E1xe2x88x92E0 greater than {fraction (1/100)}.
Also with this configuration, it is possible to decrease the critical electric field for liquid crystal transition, and achieve a quick transition from the initial alignment of the liquid crystal molecules to the bend alignment.
Here, the pretilt angle is the alignment angle of the liquid crystal molecules at the substrate surfaces before the application of an electric field, representing the tilt of the molecular axis of the liquid crystal molecules at the substrates surfaces with respect to a plane parallel to the substrates over a range of xe2x88x92xcfx80/2 to xcfx80/2 rad, and is positive in counter-clockwise direction, taking the plane parallel to the substrates as the reference (=0). Furthermore, the pretilt angle of the liquid crystal at the first substrate is marked with an opposite sign to the pretilt angle of the liquid crystal at the second substrate.
According to a fifty-third aspect of the invention, in a method for driving a liquid crystal display device as in the fiftieth aspect, the secondary electric field is applied between a source electrode or a gate electrode of a thin film transistor formed on a surface of the first substrate, and a transparent electrode formed on a surface of the second substrate.
According to a fifty-fourth aspect of the invention, in a method for driving a liquid crystal display device as in the fiftieth aspect, the secondary field is an ac electric field whose oscillation is dampened over time.